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Abstract:

A light emitting device includes: a light emitting element; and a light
variable resistive element which is connected to the light emitting
element in parallel and is provided at a position which is irradiated
with light emitted from the light emitting element, wherein the light
variable resistive element has a characteristic in which a resistance
value decreases as an amount of irradiation light increases.

Claims:

1. A light emitting device comprising: a light emitting element; and a
light variable resistive element which is connected to the light emitting
element in parallel and is provided at a position which is irradiated
with light emitted from the light emitting element, wherein the light
variable resistive element has a characteristic in which a resistance
value decreases as an amount of irradiation light increases.

2. The light emitting device according to claim 1, wherein the light
variable resistive element includes an opening portion through which a
part of the light emitted from the light emitting element passes.

3. The light emitting device according to claim 2, wherein, among the
rays of light emitted from the light emitting element, a central part of
the light passes through the opening portion, and the light variable
resistive element is irradiated with a peripheral part of the light.

5. The light emitting device according to claim 1, wherein the light
emitting element is an edge emitting type element which emits the light
from both a front end surface and a rear end surface, and the light
variable resistive element is provided at a position which is irradiated
with the light emitted from the rear end surface.

6. The light emitting device according to claim 1, further comprising: a
detection portion which is connected to the light variable resistive
element in series and detects an amount of a current which flows in the
light variable resistive element.

7. The light emitting device according to claim 1, further comprising: a
temperature variable resistive element which is connected to the light
variable resistive element in parallel, is provided so that heat of the
light emitting element can be conducted, and has a characteristic in
which the resistance value decreases as the temperature increases.

8. An image display apparatus comprising: a current source; and the light
emitting device according to claim 1.

9. An image display apparatus comprising: a current source; and the light
emitting device according to claim 2.

10. An image display apparatus comprising: a current source; and the
light emitting device according to claim 3.

11. An image display apparatus comprising: a current source; and the
light emitting device according to claim 4.

12. An image display apparatus comprising: a current source; and the
light emitting device according to claim 5.

13. An image display apparatus comprising: a current source; and the
light emitting device according to claim 6.

14. An image display apparatus comprising: a current source; and the
light emitting device according to claim 7.

Description:

BACKGROUND

[0001] 1. Technical Field

[0002] The present invention relates to a light emitting device and an
image display apparatus.

[0003] 2. Related Art

[0004] A head-mounted display (HMD) is known as a display apparatus which
directly irradiates the retina of the eyes with laser and allows a user
to visually confirm an image.

[0005] In general, the head-mounted display includes: a light emitting
device which emits light; and a scanning unit which changes an optical
path so that the emitted light is scanned on the retina of a user. By the
head-mounted display, the user can visually confirm, for example, both a
background color of the outside and the image which is drawn by the
scanning unit at the same time.

[0006] However, in the head-mounted display, since the retina is
irradiated with the light emitted from the light emitting device, it is
necessary to consider that the retina does not get damaged by the light.
In general, safety is secured by limiting an output of the light emitting
device so that an amount of the light emitted from the light emitting
device does not exceed regulatory limits.

[0007] In JP-A-6-151958, in order to control a light emitting output, a
light emitting device which is provided with a resistor which controls a
current that flows in a light emitting element is disclosed. In the light
emitting device, since an element having a characteristic of increasing a
temperature and a resistance value is used as the resistor, even if the
temperature of the light emitting element increases by self-heating or
changing of the ambient temperature, and light emitting efficiency of the
light emitting element deteriorates, it is possible to increase a ratio
of the current which flows in the light emitting element by making a
configuration in which the current that flows in the resistor is reduced
according to the temperature increase in the light emitting element. For
this reason, it is possible to compensate for the deterioration of the
light emitting efficiency, and to always obtain a predetermined light
emitting output.

[0008] However, in the display apparatus described in JP-A-6-151958, it is
possible to prevent the light emitting output from being largely
deteriorated, but it is not possible to prevent the light emitting output
from being largely increased. For this reason, if a failure or the like
is generated on a current supply circuit, and the current becomes too
high, there is a concern that the light emitting output exceeds a
presumed range.

SUMMARY

[0009] An advantage of some aspects of the invention is to provide a light
emitting device having a high level of safety in which an amount of light
is suppressed to be equal to or less than a certain value, and an image
display apparatus having a high level of safety which is provided with
the related light emitting device.

[0010] The invention can be implemented as the following application
examples.

Application Example 1

[0011] This application example is directed to a light emitting device
including: a light emitting element; and a light variable resistive
element which is connected to the light emitting element in parallel and
is provided at a position which is irradiated with light emitted from the
light emitting element. The light variable resistive element has a
characteristic in which a resistance value decreases as an amount of
irradiation light increases.

[0012] With this configuration, since an amount of light emitted from the
light emitting device can be suppressed to be equal to or less than a
certain value without using an electronic circuit or the like, a light
emitting device having a much higher level of safety can be obtained.

Application Example 2

[0013] In the light emitting device according to the application example,
it is preferable that the light variable resistive element includes an
opening portion through which a part of the light emitted from the light
emitting element passes.

[0014] With this configuration, while the part of the light passes through
the opening portion, the light variable resistive element is irradiated
with another part of the light. As a result, in the light emitting
device, it is possible to emit the light and to detect the amount of
light at the same time. Since it is not necessary to ensure an extra
space for the light variable resistive element, the size of the device
can be reduced.

Application Example 3

[0015] In the light emitting device according to the application example,
it is preferable that, among the rays of light emitted from the light
emitting element, a central part of the light passes through the opening
portion, and the light variable resistive element is irradiated with a
peripheral part of the light.

[0016] In the central part of the light, a distribution width of a
wavelength is relatively narrow, and many rays of light which are close
to ideal monochromatic light are included. For this reason, if the light
in the central part is configured to selectively pass through the opening
portion, for example, when the light emitting device is used as a light
source of the image display apparatus, it is possible to enhance color
reproducibility of an image.

Application Example 4

[0017] In the light emitting device according to the application example,
it is preferable that the light variable resistive element has optical
transparency.

[0018] With this configuration, while suppressing a decrease in the amount
of the light, it is possible to change the resistance value of the light
variable resistive element. For this reason, while securing safety of the
light emitting device, it is possible to realize a light emitting device
having a large volume of the light.

Application Example 5

[0019] In the light emitting device according to the application example,
it is preferable that the light emitting element is an edge emitting type
element which emits the light from both a front end surface and a rear
end surface, and the light variable resistive element is provided at a
position which is irradiated with the light emitted from the rear end
surface.

[0020] With this configuration, since the light emitted from the front end
surface is not influenced at all by the light variable resistive element,
the emitted light becomes light having characteristics which are
originally included in the light emitting element. For this reason, for
example, a problem, such as an insufficient amount of light is unlikely
to be generated, and the light emitting device contributes to realizing
an image display apparatus which can display an excellent image.

Application Example 6

[0021] It is preferable that the light emitting device according to the
application example further includes a detection portion which is
connected to the light variable resistive element in series and detects
an amount of a current which flows in the light variable resistive
element.

[0022] With this configuration, since the amount of the current which
flows through a line on the light emitting element side can be estimated,
it is possible to indirectly assume the amount of light of the light
emitting element. As a result, it is possible to easily find the amount
of light of the light emitting element. In addition, when the light
emitting device is embedded in the image display apparatus, in the image
display apparatus, it is possible to obtain data for comparing a current
value which is assigned to the light emitting device by the control
portion and a current value which flows in the light emitting element in
practice. For this reason, for example, it is possible to perform an
inspection for confirming an integrity of the light emitting element.

Application Example 7

[0023] It is preferable that the light emitting device according to the
application example further includes a temperature variable resistive
element which is connected to the light variable resistive element in
parallel, is provided so that heat of the light emitting element can be
conducted, and has a characteristic in which the resistance value
decreases as the temperature increases.

[0024] With this configuration, it is possible to particularly enhance
safety of the light emitting device.

Application Example 8

[0025] This application example is directed to an image display apparatus
including: a current source; and the light emitting device according to
the application example.

[0026] With this configuration, the light emitting device which can
suppress the amount of light emitted from the light emitting device to be
equal to or less than a certain value without using the electronic
circuit or the like is provided. For this reason, an image display
apparatus having a much higher level of safety can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention will be described with reference to the accompanying
drawings, wherein like numbers reference like elements.

[0028] FIG. 1 is a view illustrating a schematic configuration of an
embodiment (head-mounted display) of an image display apparatus according
to the invention.

[0030] FIG. 3 is a schematic configuration view of a signal generation
portion of the image display apparatus illustrated in FIG. 1.

[0031] FIG. 4 is a view illustrating a schematic configuration of a light
scanning portion illustrated in FIG. 1.

[0032] FIG. 5 is a view illustrating an operation of the light scanning
portion illustrated in FIG. 4.

[0033] FIG. 6 is a perspective view illustrating a schematic configuration
of a first embodiment (light source) of a light emitting device according
to the invention.

[0034] FIG. 7 is a circuit diagram illustrating an example of connection
between the light emitting device illustrated in FIG. 6 and a current
source.

[0035] FIG. 8 is a schematic view illustrating a difference of a
relationship between a driving current and an amount of light of the
light emitting element, according to a presence or an absence of a light
variable resistive element.

[0036] FIG. 9 is a perspective view illustrating a second embodiment of
the light emitting device according to the invention.

[0037] FIG. 10 is a perspective view illustrating a third embodiment of
the light emitting device according to the invention.

[0038] FIG. 11 is a perspective view illustrating a fourth embodiment of
the light emitting device according to the invention.

[0039] FIG. 12 is a perspective view illustrating a fifth embodiment of
the light emitting device according to the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0040] Hereinafter, a light emitting device and an image display apparatus
will be described in detail based on appropriate embodiments illustrated
in attached drawings.

Image Display Apparatus

[0041] First, an embodiment of the image display apparatus according to
the invention will be described.

[0042] FIG. 1 is a view illustrating a schematic configuration of the
embodiment (head-mounted display) of the image display apparatus
according to the invention. FIG. 2 is a partially enlarged view of the
image display apparatus illustrated in FIG. 1. In addition, FIG. 3 is a
schematic configuration view of a signal generation portion of the image
display apparatus illustrated in FIG. 1. FIG. 4 is a view illustrating a
schematic configuration of a light scanning portion illustrated in FIG.
1. FIG. 5 is a view illustrating an operation of the light scanning
portion illustrated in FIG. 4.

[0043] In addition, in FIG. 1, for convenience of description, an X axis,
a Y axis, and a Z axis are illustrated as three axes which are
perpendicular to each other. Tip end sides of arrows of the axes are "+
(positive)", and base end sides of the arrows of the axes are "-
(negative)". In addition, a direction which is parallel to the X axis is
an "X axis direction", a direction which is parallel to the Y axis is a
"Y axis direction", and a direction which is parallel to the Z direction
is a "Z axis direction".

[0044] Here, when an image display apparatus 1 which will be described
later is mounted on a head H of an observer, the X axis, the Y axis, and
the Z axis are set so that the Y axis direction is an up-and-down
direction of the head H, the Z axis direction is a right-and-left
direction of the head H, and the X axis direction is a front-and-rear
direction of the head H.

[0045] As illustrated in FIG. 1, the image display apparatus 1 of the
embodiment is the head-mounted display (head-mounted type image display
apparatus) which has an external appearance like glasses, is used by
being mounted on the head H of the observer, and allows the observer to
visually confirm a state where an image by a virtual image is overlapped
with an external image.

[0046] As illustrated in FIG. 1, the image display apparatus 1 is provided
with a frame 2, a signal generation portion 3, a scanned light emitting
portion 4, and a reflecting portion 6.

[0047] In addition, as illustrated in FIG. 2, the image display apparatus
1 is provided with a first optical fiber 7, a second optical fiber 8, and
a connection portion 5.

[0048] In the image display apparatus 1, the signal generation portion 3
generates signal light which is modulated according to image information,
the signal light is guided to the scanned light emitting portion 4 via
the first optical fiber 7, the connection portion 5, and the second
optical fiber 8, the scanned light emitting portion 4 emits scanned light
by scanning the signal light two-dimensionally, and the reflecting
portion 6 reflects the scanned light toward eyes EY of the observer.
Accordingly, the observer can visually confirm the virtual image
according to the image information.

[0049] In addition, in the embodiment, a case where the signal generation
portion 3, the scanned light emitting portion 4, the connection portion
5, the reflecting portion 6, the first optical fiber 7, and the second
optical fiber 8 are provided only on a right side of the frame 2, and
only the virtual image for the right eye is formed, is described as an
example. However, as a left side of the frame 2 is configured similarly
to the right side, the virtual image for the right eye and the virtual
image for the left eye may be formed together, and only the virtual image
for the left eye may be formed.

[0050] Hereinafter, each part of the image display apparatus 1 will be
described in order.

Frame

[0051] As illustrated in FIG. 1, the frame 2 is in a shape of a glasses
frame, and has a function of supporting the signal generation portion 3
and the scanned light emitting portion 4.

[0052] In addition, as illustrated in FIG. 1, the frame 2 includes: a
front portion 22 which supports the scanned light emitting portion 4 and
a nose pad portion 21; a pair of temple portions (hooking portions) 23
which abuts against the ears of a user by being connected to the front
portion 22; and a modern portion 24 which is an end portion of each
temple portion 23 opposite to the front portion 22.

[0053] The nose pad portion 21 abuts against a nose NS of the observer
when the apparatus is in use, and supports the image display apparatus 1
with respect to the head of the observer. The front portion 22 includes a
rim portion 25 or a bridge portion 26.

[0054] The nose pad portion 21 is configured to be capable of adjusting a
position of the frame 2 with respect to the observer when the apparatus
is in use.

[0055] In addition, if the apparatus can be mounted on the head H of the
observer, the shape of the frame 2 is not limited to that in the drawing.

Signal Generation Portion

[0056] As illustrated in FIG. 1, the signal generation portion 3 is
provided in the modern portion 24 (end portion on a side opposite to the
front portion 22 of the temple portion 23) of one side (right side in the
embodiment) of the frame 2 described above.

[0057] In other words, the signal generation portion 3 is disposed on the
side opposite to the eyes EY with respect to the ears EA of the observer
when the apparatus is in use. Accordingly, a weight balance of the image
display apparatus 1 can be excellent.

[0058] The signal generation portion 3 has a function of generating the
signal light which is scanned by a light scanning portion 42 of the
scanned light emitting portion 4 which will be described later, and a
function of generating a driving signal which drives the light scanning
portion 42.

[0059] As illustrated in FIG. 3, the signal generation portion 3 is
provided with a signal light generation portion 31, a driving signal
generation portion 32, a control portion 33, an optical detection portion
34, and a fixing portion 35.

[0060] The signal light generation portion 31 generates the signal light
which is scanned (scanned light) by the light scanning portion 42
(optical scanner) of the scanned light emitting portion 4 which will be
described later.

[0061] The signal light generation portion 31 has: a plurality of light
sources 311R, 311G, and 311B (light source portions) which have different
wavelengths from each other; a plurality of driving circuits 312R, 312G,
and 312B; lenses 313R, 313G, and 313B; and a light combining portion
(combining portion) 314.

[0063] The light sources 311R, 311G, and 311B are provided with a light
emitting device (to be described later) according to the invention. In
addition, the light emitting device will be described later.

[0064] The light sources 311R, 311G, and 311B are electrically connected
to the driving circuits 312R, 312G, and 312B, respectively.

[0065] The driving circuit 312R has a function of driving the light source
311R described above, the driving circuit 312G has a function of driving
the light source 311G described above, and the driving circuit 312B has a
function of driving the light source 311B described above.

[0066] The three types (three colors) of light which are emitted from the
light sources 311R, 311G, and 311B that are driven by the driving
circuits 312R, 312G, and 312B, are incident on the light combining
portion 314 via the lenses 313R, 313G, and 313B.

[0067] The lenses 313R, 313G, and 313B are respectively collimator lenses.
Accordingly, the light emitted from the light sources 311R, 311G, and
311B are respectively formed to be parallel light, and are respectively
incident on the light combining portion 314.

[0068] The light combining portion 314 combines the light from the
plurality of light sources 311R, 311G, and 311B. Accordingly, the number
of the optical fibers for transmitting the signal light generated by the
signal light generation portion 31 to the scanned light emitting portion
4, can be small. For this reason, in the embodiment, it is possible to
transmit the signal light from the signal generation portion 3 to the
scanned light emitting portion 4 via one light transmission path which is
formed of the first optical fiber 7, the connection portion 5 and the
second optical fiber 8.

[0069] In the embodiment, the light combining portion 314 has three
dichroic mirrors 314a, 314b, and 314c, and emits one ray of signal light
by combining the rays of the light (three colors of light, such as the
red light, the green light, and the blue light) emitted from the light
sources 311R, 311G, and 311B. In addition, hereinafter, the light sources
311R, 311G, and 311B are all together referred to as a "light source
portion 311". The signal light generated by the signal light generation
portion 31 is referred to as "light emitted from the light source portion
311".

[0070] In addition, the configuration of the light combining portion 314
is not limited to the configuration in which the above-described dichroic
mirrors are used, and for example, may be a configuration in which a
prism, an optical waveguide, or an optical fiber is used.

[0071] The signal light generated by the signal light generation portion
31 is incident on one end portion of the first optical fiber 7. Then, the
signal light passes through the first optical fiber 7, the connection
portion 5, and the second optical fiber 8 in order, and is transmitted to
the light scanning portion 42 of the scanned light emitting portion 4
which will be described later.

[0072] Here, in the vicinity of the end portion (hereinafter, simply
referred to as "one end portion of the first optical fiber 7) of an
incident side of the signal light of the first optical fiber 7, the
optical detection portion 34 is provided. The optical detection portion
34 detects the signal light. In addition, one end portion of the first
optical fiber 7 and the optical detection portion 34 are fixed to the
fixing portion 35.

[0073] The driving signal generation portion 32 generates the driving
signal which drives the light scanning portion 42 (optical scanner) of
the scanned light emitting portion 4 which will be described later.

[0074] The driving signal generation portion 32 includes: a driving
circuit 321 (first driving circuit) which generates a first driving
signal that is used in scanning (horizontal scanning) in a first
direction of the light scanning portion 42; and a driving circuit 322
(second driving circuit) which generates a second driving signal that is
used in scanning (vertical scanning) in a second direction orthogonal to
the first direction of the light scanning portion 42.

[0075] The driving signal generation portion 32 is electrically connected
to the light scanning portion 42 of the scanned light emitting portion 4
which will be described later, via a signal line (not illustrated).
Accordingly, the driving signal (the first driving signal and the second
driving signal) generated by the driving signal generation portion 32 is
input into the light scanning portion 42 of the scanned light emitting
portion 4 which will be described later.

[0076] The above-described driving circuits 312R, 312G, and 312B of the
signal light generation portion 31 and the driving circuits 321 and 322
of the driving signal generation portion 32, are electrically connected
to the control portion 33.

[0077] The control portion 33 has a function of controlling the driving of
the driving circuits 312R, 312G, and 312B of the signal light generation
portion 31 and the driving circuits 321 and 322 of the driving signal
generation portion 32, based on a video signal (image signal). In other
words, the control portion 33 has a function of controlling the driving
of the scanned light emitting portion 4. Accordingly, the signal light
generation portion 31 generates the signal light which is modulated
according to the image information, and the driving signal generation
portion 32 generates the driving signal according to the image
information.

[0078] In addition, the control portion 33 is configured to be capable of
controlling the driving of the driving circuits 312R, 312G, and 312B of
the signal light generation portion 31, based on an intensity of light
detected by the optical detection portion 34.

Scanned Light Emitting Portion

[0079] As illustrated in FIGS. 1 and 2, the scanned light emitting portion
4 is installed in the vicinity (that is, the vicinity of the center of
the front portion 22) of the bridge portion 26 of the above-described
frame 2.

[0080] As illustrated in FIG. 4, the scanned light emitting portion 4 is
provided with a housing 41 (case), a light scanning portion 42, a lens 43
(coupling lens), a lens 45 (condenser lens), and a supporting member 46.

[0081] The housing 41 is installed in the front portion 22 via the
supporting member 46.

[0082] In addition, an outer surface of the housing 41 is bonded to a part
on a side opposite to the frame 2 of the supporting member 46.

[0083] The housing 41 supports the light scanning portion 42 and
accommodates the light scanning portion 42. In addition, the lens 43 and
the lens 45 are installed in the housing 41, and the lens 43 and the lens
45 constitute a part (a part of a wall portion) of the housing 41.

[0084] In addition, the lens 43 (window portion through which the signal
light of the housing 41 goes) is separated from the second optical fiber
8. In the embodiment, the end portion on the emitting side of the signal
light of the second optical fiber 8 is positioned to face a reflecting
portion 10 provided in the front portion 22 of the frame 2, and is
separated from the scanned light emitting portion 4.

[0085] The reflecting portion 10 has a function of reflecting the signal
light emitted from the second optical fiber 8 toward the light scanning
portion 42. In addition, the reflecting portion 10 is provided in a
concave portion 27 which is open to an inner side of the front portion
22. In addition, the opening of the concave portion 27 may be covered by
the window portion which is configured by a transparent material. In
addition, if the signal light can be reflected, the configuration of the
reflecting portion 10 is not particularly limited. For example, the
reflecting portion 10 can be configured by a mirror, a prism, or the
like.

[0086] The light scanning portion 42 is the optical scanner which scans
the signal light from the signal light generation portion 31
two-dimensionally. As the signal light is scanned by the light scanning
portion 42, the scanned light is formed. Specifically, the signal light
emitted from the second optical fiber 8 is incident on a light reflecting
surface of the light scanning portion 42 via the lens 43. According to
the driving signal generated by the driving signal generation portion 32,
as the light scanning portion 42 is driven, the signal light is scanned
two-dimensionally.

[0087] In addition, the light scanning portion 42 has a coil 17 and a
signal superposition portion 18 (refer to FIG. 4), and the coil 17, the
signal superposition portion 18, and the driving signal generation
portion 32 constitute a driving portion which drives the light scanning
portion 42.

[0088] The lens 43 has a function of adjusting a spot diameter of the
signal light emitted from the first optical fiber 7. In addition, the
lens 43 has a function of adjusting a radiation angle of the signal light
emitted from the first optical fiber 7 and substantially parallelizes the
angle.

[0089] The signal light (scanned light) scanned by the light scanning
portion 42 is emitted to the outside of the housing 41 via the lens 45.

Reflecting Portion

[0090] As illustrated in FIGS. 1 and 2, the reflecting portion 6 is
installed in the rim portion 25 which is included in the front portion 22
of the above-described frame 2.

[0091] In other words, the reflecting portion 6 is disposed to be
positioned on a front side of the eyes EY of the observer when the
apparatus is in use, and on a side far from the observer even further
than the light scanning portion 42. Accordingly, a part which is
projected to the front side of the face of the observer in the image
display apparatus 1 can be prevented from being formed.

[0092] As illustrated in FIG. 5, the reflecting portion 6 has a function
of reflecting the signal light from the light scanning portion 42 toward
the eyes of the observer.

[0093] In the embodiment, the reflecting portion 6 is a half mirror, and
even has a function (translucency with respect to visible light) of
making external light go through. In other words, the reflecting portion
6 reflects the signal light from the light scanning portion 42, and has a
function of making the external light go through toward the eyes of the
observer from the outside of the reflecting portion 6 when the apparatus
is in use. Accordingly, the observer can visually confirm the virtual
image (image) which is formed by the signal light, while the observer
visually confirms the external image. In other words, it is possible to
realize a see-through type head-mounted display.

[0094] In addition, the reflecting portion 6 may have a diffraction
grating, for example. In this case, by giving various optical properties
to the diffraction grating, it is possible to reduce the number of
components of an optical system, or to enhance flexibility of design. For
example, as a hologram element is used as the diffraction grating, it is
possible to adjust an emitting direction of the signal light which is
reflected by the reflecting portion 6. In addition, by giving a lens
effect to the diffraction grating, it is possible to adjust an imaging
state of the entire scanned light which is formed from the signal light
reflected by the reflecting portion 6.

[0095] In addition, the reflecting portion 6 may form a semi-transmissive
reflecting film which is configured, for example, by a metal thin film or
a dielectric multilayer film on a transparent substrate.

[0097] The fixing portion 35 has a function of fixing one end portion of
the first optical fiber 7 to a position at which the intensity of the
light incident on the first optical fiber 7 from the light source portion
311 is greater than zero and equal to or less than a predetermined value.
Accordingly, it is possible to make the intensity of the light incident
on the first optical fiber 7 from the light source portion 311 small.

[0098] In addition, the fixing portion 35 has a function of fixing the
optical detection portion 34. Accordingly, it is possible to efficiently
use remaining light which is not incident on the first optical fiber 7
among the rays of light (signal light) emitted from the light source
portion 311, in the detection of the optical detection portion 34. In
addition, it is possible to fix (constantly maintain) a positional
relationship between one end portion of the first optical fiber 7 and the
optical detection portion 34.

[0099] Even when the optical detection portion 34 fixed to the fixing
portion 35 in this manner is not provided with the optical system which
makes the signal light emitted from the light sources 311B, 311G, and
311R diverge, it is possible to detect the intensity of the emitted light
by the optical detection portion 34. In addition, based on the intensity
of the light detected by the optical detection portion 34, it is possible
to adjust the intensity of the light emitted from the light sources 311B,
311G, and 311R by the control portion 33. In addition, the control
portion 33 is configured by a "light control portion" which controls the
light sources 311B, 311G, and 311R.

[0100] In addition, the embodiment of the image display apparatus
according to the invention is not limited to an embodiment having a
retina scanning type display principle, such as the above-described
head-mounted display. In other words, the embodiment of the image display
apparatus according to the invention may have a display principle other
than the retina scanning type, such as a heads-up display, a laser
projector, or a laser television. Even in a case of these display
principles, there is a concern that reflected light is incident on the
retina indirectly and coincidently. Therefore, by the invention, it is
possible to expect similar operations and effects to a case of the retina
scanning type.

Light Emitting Device

First Embodiment

[0101] Next, a first embodiment of the light emitting device according to
the invention will be described.

[0102] FIG. 6 is a perspective view illustrating a schematic configuration
of a first embodiment (light source) of the light emitting device
according to the invention. FIG. 7 is a circuit diagram illustrating an
example of connection between the light emitting device illustrated in
FIG. 6 and a current source. In addition, in the description below, an
upside of FIG. 6 will be described as "up", and a downside of FIG. 6 will
be described as "down".

[0103] The above-described light sources 311R, 311G, and 311B are
respectively configured by the embodiments of the light emitting device
according to the invention.

[0105] In addition, as illustrated in FIG. 7, the light emitting element
91 and the light variable resistive element 97 are connected to each
other in parallel. In addition, an anode of the light emitting element 91
is connected to a current source 99, and is electrically grounded to a
cathode side. In addition, the current source 99 corresponds to each
current source which is provided in the above-described plurality of
driving circuits 312R, 312G, and 312B.

Mounting Substrate

[0106] The mounting substrate 94 is a substrate for mounting the mount 93
on which the light emitting element 91 and the light variable resistive
element 97 are loaded.

[0107] The mounting substrate 94 is provided with an insulating substrate
941 and two external electrode terminals 942 and 943 provided on the
surface thereof. In addition, although not illustrated in the drawing,
there is provided a wiring which is connected to the external electrode
terminals 942 and 943. The light emitting element 91 and the current
source 99 are connected to each other via the external electrode
terminals 942 and 943.

[0108] In addition, the mounting substrate 94 can be provided as
necessary, and can be omitted.

Mount

[0109] The mount 93 is used as a foundation on which the light emitting
element 91 is mounted. In general, the mount is configured by a material
having a high thermal conductivity, and has a function of dissipating the
heat generated by the light emitting element 91 at high efficiency. In
addition, the mount 93 also has high insulation properties, and has a
function of ensuring the insulation with the light emitting element 91
and a heat sink (not illustrated) or the like. Accordingly, it is
possible to stabilize the light emitting of the light emitting element
91.

[0110] As a configuration material of the mount 93, for example, a
ceramics material, such as aluminum nitride or silicon carbide, and a
metal material, such as copper or aluminum, can be used. In addition, as
necessary, the mount 93 is configured by a composite in which a metal
layer is formed on one surface or on both surfaces of the substrate made
of the ceramics material.

[0111] In addition, the heat sink (not illustrated) may be provided
between the mount 93 and the mounting substrate 94.

[0112] In addition, the mount 93 can be provided as necessary, and can be
omitted in a case where the amount of heat from the light emitting
element 91 is small, or the like.

Light Emitting Element

[0113] Examples of the light emitting element 91 include a semiconductor
laser (LD), a super luminescent diode (SLD), a light emitting diode
(LED), an organic EL element, an inorganic EL element, or the like.
However, an edge emitting type semiconductor laser is illustrated as an
example in FIG. 6.

[0114] In general, a structure of the semiconductor laser is a chip
structure in which an electrode or the like is installed on a laminated
body which is made by laminating layers configured by a semiconductor
material, and has a shape of a rectangular parallelepiped or a shape
which is equivalent thereto. The edge emitting type semiconductor laser
has a configuration in which a resonator for resonating the light is
parallel to a semiconductor substrate surface. The reflecting surfaces of
the resonator are two cleavage planes of the semiconductor substrate. As
the light is extracted from one cleavage plane, the laser is emitted.

[0115] The light emitting element 91 illustrated in FIG. 6 has: a
semiconductor portion 911 which is configured by the laminated body
including an n-type semiconductor layer, an active layer, and a p-type
semiconductor layer; a lower electrode 912 which is provided on a lower
side of the semiconductor portion 911; and an upper electrode 913 which
is provided on an upper side of the semiconductor portion 911. The lower
electrode 912 and the upper electrode 913 are respectively configured by
conductor layers.

[0116] The light emitting element 91 is loaded on the mount 93.
Accordingly, the lower electrode 912 is interposed between the
semiconductor portion 911 and the mount 93. In addition, the lower
electrode 912 extends along a longitudinal direction of the light
emitting element 91 and along an upper surface of the mount 93, to be
protruded from the semiconductor portion 911. Meanwhile, a width of the
upper electrode 913 is narrower than a width of the semiconductor portion
911.

[0117] In addition, the lower electrode 912 and the external electrode
terminal 942 are electrically connected to each other via a bonding wire
981. Meanwhile, the upper electrode 913 and the external electrode
terminal 943 are electrically connected to each other via a bonding wire
982. Among the external electrode terminal 942 and the external electrode
terminal 943, if the current flows to the anode side of the light
emitting element 91, the light is emitted from an emitting portion 910 of
the light emitting element 91. In a case of the semiconductor laser, as a
composition of the semiconductor material which constitutes the
semiconductor portion 911 is changed, it is possible to select a
wavelength (color) of the emitted light.

[0118] In addition, in the description above, the lower electrode 912, the
upper electrode 913, and the semiconductor portion 911 are all together
considered as the light emitting element 91. However, examples of the
light emitting element 91 is not limited thereto, and for example, a
conductive material, such as an AuSn eutectic solder, may be interposed
between the lower electrode 912 and the semiconductor portion 911.

[0119] In addition, when the mount 93 is made of a metal material or when
the mount 93 is made of a ceramics material provided with a metal layer
on a surface thereof, since the metal portions function as an electrode,
it is possible to omit the lower electrode 912.

Light Variable Resistive Element

[0120] The light variable resistive element 97 according to the embodiment
is a resistive element having a characteristic in which a resistance
value decreases as the amount of irradiation light increases. Examples of
the resistive element having such a characteristic include a
photoresistor, an intrinsic semiconductor element, an impurity
semiconductor element, or the like. Among these examples, by using the
photoresistor, it is possible to change the resistance value since an
amount of electric charge changes according to the amount of light by an
internal photoelectric effect of a compound semiconductor. For example,
when the amount of light which irradiates the photoresistor increases,
the amount of electric charge increases, and thus, the resistance value
decreases. Examples of the compound semiconductor which is used in the
photoresistor include cadmium sulfide (Cds), lead sulfide (PdS), lead
selenide (PbSe), or the like. However, in the viewpoint of a
responsiveness in the visible light, it is preferable to use the cadmium
sulfide.

[0121] In the embodiment, light L is emitted from the emitting portion 910
of the light emitting element 91, but the light variable resistive
element 97 is provided at a position facing the emitting portion 910. For
this reason, when the light L is emitted from the emitting portion 910,
the light variable resistive element 97 is irradiated with the light L.

[0122] Meanwhile, the light variable resistive element 97 according to the
embodiment is in a flat board shape as illustrated in FIG. 6, and the
shape in a planar view thereof is a substantial square. In addition, the
shape thereof is not particularly limited.

[0123] In addition, the light variable resistive element 97 has: a light
detection portion 971 in which the irradiation light is applied to the
resistance value; an opening portion 972 through which the light variable
resistive element 97 passes in a thickness direction; and a pair of
terminal electrodes 973 and 974 provided in the light detection portion
971. The light variable resistive element 97 is disposed at a position
where the light L emitted from the light emitting element 91 can pass
through the opening portion 972. In other words, the light L is emitted
to the outside of the light emitting device 9 via the opening portion
972.

[0124] Here, the light L emitted from the light emitting element 91 is
usually transferred as a ray of light having a predetermined flare angle.
For this reason, when the light variable resistive element 97 is
irradiated with the light L, an irradiation area 975 illustrated in FIG.
6 is generated. At this time, if the opening portion 972 is disposed on
an inner side of the range of the irradiation area 975, at least a part
of the light L can pass through the opening portion 972.

[0125] In the embodiment, the position of the light variable resistive
element 97 and the size of the opening portion 972 are set so that the
opening portion 972 is disposed on the inner side of the irradiation area
975 and an area of the irradiation area 975 is greater than an area of
the opening portion 972. By setting in this manner, while a part of the
light L passes through the opening portion 972, the light detection
portion 971 is irradiated with another part of the light L. As a result,
in the light emitting device 9, it is possible to perform both the
emission of the light L and the detection of the amount of light L at the
same time. Since it is not necessary to ensure an extra space for light
variable resistive element 97, the size of the apparatus can be reduced.

[0126] When the light detection portion 971 is irradiated with the light,
the resistance value of the light detection portion 971 decreases
according to the amount of irradiation light by the internal
photoelectric effect.

[0127] As described above, the light emitting element 91 and the light
variable resistive element 97 are connected to each other in parallel.
For this reason, the current, which flows through a line on the light
emitting element 91 side before the increase in the amount of light,
flows through a line on the light variable resistive element 97 side as
the resistance value of the light variable resistive element 97 decreases
after the increase in the amount of light. As a result, the current which
flows through the line on the light emitting element 91 side decreases.

[0128] In the semiconductor laser or the like, since the driving current
and the amount of light is in a substantially proportional relationship,
when the current which flows through the line on the light emitting
element 91 side decreases, the amount of light of the light emitting
element 91 decreases. Accordingly, the amount of light of the light
emitting element 91 is prevented from being increased any more.

[0129] In addition, as described above, the light L is transferred as a
ray of light having a predetermined flare angle. For this reason, at a
time of adjusting a size relationship between the area of the opening
portion 972 and the area of the irradiation area 975, the distance
between the light emitting element 91 and the light variable resistive
element 97 may be changed.

[0130] The above-described behavior is based on basic characteristics of
the light variable resistive element 97 which is one of passive elements,
and differs from a behavior based on an operation of an active element
which is called an IC including an electronic circuit. In addition, the
light variable resistive element 97 can be considered as an element
having a high tolerance with respect to an environment change, such as a
temperature change or a shock, compared to the IC or the like, and having
an extremely low failure probability. For this reason, according to the
embodiment, it is possible to suppress the amount of the light emitted
from the light emitting element 91 to be equal to or lower than a certain
value without following a calculation or the like. Therefore, it is
possible to sufficiently secure safety of the light emitting device 9. In
other words, in the image display apparatus 1 which causes the signal
light to be directly incident toward the eyes EY of the observer, even if
the current which flows in the light emitting element 91 is extremely
high, since the current can be quickly suppressed and the amount of light
can be suppressed to be equal to or less than the certain amount, it is
possible to suppress an adverse effect on the retina of the observer to a
minimum.

[0131] FIG. 8 is a schematic view illustrating a difference of a
relationship between the driving current and the amount of light of the
light emitting element, according to a presence or an absence of the
light variable resistive element. In addition, a dotted line R1
illustrated in FIG. 8 is a line illustrating an example of an upper limit
of the amount of light which does not have an adverse effect on the
retina. In addition, a dotted line R2 illustrated in FIG. 8 is a line
illustrating an example of the upper limit of the amount of light which
is used at a normal time in the image display apparatus 1.

[0132] When the light variable resistive element 97 is not provided, as
the current which flows in the light emitting element 91 increases, the
amount of the light emitted from the light emitting element 91 increases
substantially being proportional to the current, as illustrated as a
solid line L1. For this reason, when the solid line L1 exceeds the dotted
line R1, there is a concern about an adverse effect on the retina.

[0133] Meanwhile, even when the light variable resistive element 97 is
provided, as illustrated as a solid line L2 in FIG. 8, at first, as the
current which flows in the light emitting element 91 increases, the
amount of light increases. However, since the current which flows in the
light emitting element 91 decreases as the amount of light increases, a
ratio of increase in the amount of light gradually deteriorates. Finally,
the amount of light reaches a state where the amount of light converges
on a certain value, or a state (saturated state) where the amount of
light is stuck in an extremely slight increase. At this time, it is
possible to adjust the saturation level of the amount of light by
appropriately selecting an element having a different relationship
between the change in the amount of light irradiating the light detection
portion 971 and the resistance value change. Therefore, if the solid line
L2 is set not to exceed the dotted line R1, it is possible to realize the
light emitting device 9 which sufficiently secures safety.

[0134] In addition, there is a surface mounting type photoresistor or a
reed type photoresistor. However, any type of photoresistor may be used.

[0135] In addition, in the embodiment, a part of the light L passes
through the opening portion 972, and the light detection portion 971 is
irradiated with another part of the light. However, it is preferable that
a part of the light L which passes through the opening portion 972 be
light which corresponds to a central part of a cross section in the light
L. In the central part of the cross section of the light L, a
distribution width of the wavelength is relatively narrow, and many rays
of light which are close to ideal monochromatic light are included. For
this reason, if the light in the central part is configured to
selectively pass through the opening portion 972, for example, when the
light emitting device 9 is used as a light source of the image display
apparatus 1, it is possible to enhance color reproducibility of an image.

[0136] Meanwhile, in a peripheral part of the cross section of the light
L, there is a case where the distribution width of the wavelength is
relatively wide and relatively many rays of light of a wavelength other
than a peak wavelength is included. For this reason, if the light
detection portion 971 is irradiated with the peripheral part of the
light, for example, it is possible to enhance color reproducibility of
the image display apparatus 1, and to sufficiently secure safety of the
image display apparatus 1.

[0137] In addition, in the light variable resistive element 97, a speed of
applying the change of the amount of irradiation light to the change of
the resistance value, that is, a response speed is relatively high
compared to other variable resistive elements. For this reason, when the
amount of light L exceeds the certain value, the resistance value of the
light variable resistive element 97 quickly decreases, and accordingly,
the amount of light of the light emitting element 91 quickly decreases.
For this reason, after the amount of light of the light emitting element
91 exceeds the certain value, a time lag until the resistance value of
the light variable resistive element 97 is sufficiently small and the
current decreases to an extent that the amount of light of the light
emitting element 91 is lower than the certain value, is reduced. This
also causes the time for emitting the light having an amount that
adversely affects the retina to be a minimum. Accordingly, it is possible
to further enhance safety of the light emitting device 9.

[0138] In addition, the terminal electrode 973 and the lower electrode 912
of the light emitting element 91 are electrically connected to each other
via a bonding wire 983. Meanwhile, the terminal electrode 974 and the
upper electrode 913 of the light emitting element 91 are electrically
connected to each other via a bonding wire 984. As the light variable
resistive element 97 and the light emitting element 91 are connected to
each other in parallel in this manner, as described above, without
largely changing voltage applied to the light emitting element 91, it is
possible to reduce the current which flows in the light emitting element
91. For this reason, it is possible to achieve both a stable light
emitting and a safety securing of the light emitting element 91.

[0139] In addition, in the light emitting device 9 illustrated in FIG. 6,
both the light emitting element 91 and the light variable resistive
element 97 are mounted on the mount 93. For this reason, the heat
generated from the light emitting element 91 can be conducted to the
mount 93, and it is possible to efficiently dissipate the heat from the
light emitting element 91. Furthermore, a generation of a failure, such
as a significant increase in the temperature of the light variable
resistive element 97 and an unintentional change in the resistance value,
can be suppressed.

[0140] In addition, the position of the light variable resistive element
97 is not limited to the above-described position, and for example, the
light variable resistive element 97 may be mounted on the mounting
substrate 94.

Second Embodiment

[0141] Next, a second embodiment of the light emitting device according to
the invention will be described.

[0142] FIG. 9 is a perspective view illustrating the second embodiment of
the light emitting device according to the invention.

[0143] Hereinafter, the second embodiment will be described, but in the
description below, differences from the above-described first embodiment
will be mainly described, and similar parts and the description thereof
will be omitted. In addition, in the drawing, the same configuration as
that of the above-described embodiment is given the same reference
numerals.

[0144] The second embodiment is similar to the first embodiment except
that the structure of the light variable resistive element 97 is
different.

[0145] In the light variable resistive element 97 according to the second
embodiment, the light detection portion 971 has optical transparency, and
the opening portion 972 illustrated in FIG. 9 is omitted. When the light
variable resistive element 97 is irradiated with the light L, the light L
goes through the light detection portion 971. At this time, the light L
causes a change in the resistance value by the internal photoelectric
effect in the light detection portion 971. Meanwhile, the light L which
does not contribute to the internal photoelectric effect goes through the
light detection portion 971 and is emitted from the light emitting device
9.

[0146] By this configuration, while suppressing the decrease in the amount
of light of the light L, it is possible to change the resistance value of
the light variable resistive element 97. For this reason, while securing
safety of the light emitting device 9, it is possible to realize the
light emitting device 9 having a large amount of light.

[0147] In addition, example of the light variable resistive element 97
having optical transparency includes a light variable resistive element
in which an electrode portion of the photoresistor is replaced with a
transparent electrode. In a common photoresistor, two electrodes are
disposed via a compound semiconductor, and a metal material having an
excellent conductivity, such as aluminum or the like, is used as a
configuration material of the electrode. The electrode portion is
configured by a transparent conductive material, such as indium tin oxide
(ITO), fluorine-doped tin oxide (FTO), or tin oxide (TO). Accordingly,
optical transparency is given to a part other than the compound
semiconductor.

[0148] Therefore, as the alignment of the light variable resistive element
97 is determined so that the compound semiconductor is irradiated with a
part of the cross section of the light L, most of the light L can go
through the light variable resistive element 97.

[0149] Even in the second embodiment, similar operations and effects to
those of the first embodiment can be obtained.

Third Embodiment

[0150] Next, a third embodiment of the light emitting device according to
the invention will be described.

[0151] FIG. 10 is a perspective view illustrating the third embodiment of
the light emitting device according to the invention.

[0152] Hereinafter, the third embodiment will be described, but in the
description below, differences from the above-described first and second
embodiments will be mainly described, and similar parts and the
description thereof will be omitted. In addition, in the drawing, the
same configuration as that of the above-described embodiment is given the
same reference numerals.

[0153] The third embodiment is also similar to the first embodiment except
that the alignment of the light variable resistive element 97 is
different.

[0154] The shape in a planar view of the light emitting element 91
illustrated in FIG. 10 is a rectangle (oblong), and the emitting portion
910 which emits the light L is provided in a first side surface
corresponding to a first side 914 of the rectangle. In addition, the
first side surface which is provided with the emitting portion 910 is
usually called a front end surface.

[0155] When the light emitting element 91 is the end surface light
emitting type semiconductor laser, there is not only an element of a type
in which the light is emitted from the front end surface (first side
surface) but also an element of a type in which light L' is emitted from
a second side surface which is positioned on a side opposite to the first
side surface. The second side surface is usually called a rear end
surface. In the light emitting device 9 illustrated in FIG. 10, the light
variable resistive element 97 is disposed to correspond not to the front
end surface of the light emitting element 91, but to the rear end surface
of the light emitting element 91.

[0156] An amount of the light L' emitted from the rear end surface has a
certain correlation with the amount of the light L emitted from the front
end surface. For this reason, as the light variable resistive element 97
is irradiated with the light L' emitted from the rear end surface, it is
possible to adjust the current which flows in the light emitting element
91 so that the light L emitted from the front end surface does not exceed
regulatory limits.

[0157] In other words, since the light L emitted from the front end
surface does not influence the light variable resistive element 97 at
all, the emitted light becomes light having characteristics which are
originally included in the light emitting element 91. For this reason,
for example, a problem, such as an insufficient amount of light, is
unlikely to be generated, and the light emitting device 9 contributes to
realizing the image display apparatus 1 which is capable of displaying an
excellent image.

[0158] In addition, in the embodiment, the opening portion 972 of the
light variable resistive element 97 is not necessary.

[0159] Even in the third embodiment, similar operations and effects to
those of the first embodiment can be obtained.

Fourth Embodiment

[0160] Next, a fourth embodiment of the light emitting device according to
the invention will be described.

[0161] FIG. 11 is a perspective view illustrating the fourth embodiment of
the light emitting device according to the invention.

[0162] Hereinafter, the fourth embodiment will be described, but in the
description below, differences from the above-described first to third
embodiments will be mainly described, and similar parts and the
description thereof will be omitted. In addition, in the drawing, the
same configuration as that of the above-described embodiment is given the
same reference numerals.

[0163] The fourth embodiment is similar to the third embodiment except
that the resistive element 96 which is connected to the light variable
resistive element 97 in series is provided.

[0164] As illustrated in FIG. 11, the light emitting device 9 according to
the fourth embodiment is provided with the resistive element 96 which is
mounted on the mount 93.

[0165] The resistive element 96 illustrated in FIG. 11 has: a resistance
portion 961; a terminal electrode 962 which is provided at one end
thereof; and a terminal electrode 963 which is provided at the other end
thereof. The terminal electrode 974 of the light variable resistive
element 97 and the terminal electrode 963 of the resistive element 96 are
electrically connected to each other via a bonding wire 985. Meanwhile,
the upper electrode 913 of the light emitting element 91 and the terminal
electrode 962 of the resistive element 96 are electrically connected to
each other via a bonding wire 986.

[0166] As the resistive element 96 is connected to the light variable
resistive element 97 in series, the resistive element 96 functions as the
detection portion which detects the amount of the current which flows in
the light variable resistive element 97. In other words, when the current
flows through the line on the light variable resistive element 97 side, a
potential difference is generated according to the resistance value
between the terminal electrodes of the resistive element 96. For this
reason, as the potential difference is measured, it is possible to
estimate the amount of the current which flows in the light variable
resistive element 97.

[0167] As the size of the current is detected in this manner, the size of
the current which flows through the line on the light emitting element 91
side can be estimated. For this reason, it is possible to indirectly
assume the amount of light of the light emitting element 91. Accordingly,
it is possible to easily find the amount of light of the light emitting
element 91. In addition, in the image display apparatus 1, since data for
comparing a current value assigned to the light source by the control
portion 33 and a current value which flows in the light emitting element
91 can be acquired, it is possible to perform the detection which is
called confirming an integrity of the light emitting element 91, for
example.

[0168] In addition, there is a case where the resistive element 96 is
called a shunt. The resistance value varies according to the voltage or
the current applied to the circuit, but is set to be equal to or less
than 10Ω, for example.

[0169] Even in the fourth embodiment, similar operations and effects to
those of the first embodiment can be obtained.

Fifth Embodiment

[0170] Next, a fifth embodiment of the light emitting device according to
the invention will be described.

[0171] FIG. 12 is a perspective view illustrating the fifth embodiment of
the light emitting device according to the invention.

[0172] Hereinafter, the fifth embodiment will be described, but in the
description below, differences from the above-described first to fourth
embodiments will be mainly described, and similar parts and the
description thereof will be omitted. In addition, in the drawing, the
same configuration as that of the above-described embodiment is given the
same reference numerals.

[0173] The fifth embodiment is similar to the first embodiment except that
the temperature variable resistive element 92 which is connected to the
light variable resistive element 97 in parallel is further provided.

[0174] As illustrated in FIG. 12, the light emitting device 9 according to
the fifth embodiment is provided with the temperature variable resistive
element 92 which is mounted on the mount 93. The temperature variable
resistive element 92 is a resistive element having a characteristic in
which the resistance value decreases as the temperature increases.
Examples of the resistive element having such a characteristic include an
NTC thermistor, a CTR thermistor, or the like. Among these, it is
preferable to use the NTC thermistor which is easily made small and has
high responsiveness.

[0175] In the embodiment, the light emitting element 91 and the
temperature variable resistive element 92 are disposed to be close to
each other so that the heat conduction between the light emitting element
91 and the temperature variable resistive element 92 can be performed
easily. For this reason, when the heat is generated as the light emitting
element 91 is driven, the heat is conducted to the temperature variable
resistive element 92, and the temperature of the temperature variable
resistive element 92 increases. When the temperature of the temperature
variable resistive element 92 increases, the resistance value of the
element decreases based on the above-described characteristics.

[0176] As described above, the light variable resistive element 97 and the
temperature variable resistive element 92 are connected to each other in
parallel. Therefore, the temperature variable resistive element 92 is
connected even to the light emitting element 91 in parallel. For this
reason, the current, which flows through a line on the light emitting
element 91 side before the increase in the temperature, flows through a
line on the temperature variable resistive element 92 side as the
resistance value of the temperature variable resistive element 92
decreases after the increase in the temperature. As a result, the current
which flows through the line on the light emitting element 91 side
decreases.

[0177] The above-described behavior is based on basic characteristics of
the temperature variable resistive element which is one of passive
elements. Therefore, the temperature variable resistive element 92 can be
considered as an element having a high tolerance with respect to an
environment change, such as a temperature change or a shock, compared to
the IC or the like, and having an extremely low failure probability.

[0178] For this reason, the temperature variable resistive element 92,
together with the light variable resistive element 97, can suppress the
amount of light emitted from the light emitting element 91 to be equal to
or less than a certain value, and can more reliably secure safety of the
light emitting device 9. In other words, in the image display apparatus 1
which causes the signal light to be directly incident toward the eyes EY
of the observer, even if the current which flows in the light emitting
element 91 is extremely high, since the current can be quickly suppressed
and the amount of light can be suppressed to be equal to or less than the
certain amount, it is possible to suppress an adverse effect on the
retina of the observer to a minimum.

[0179] In addition, there is a chip type or a reed type of the NTC
thermistor. In particular, it is preferable to use the chip type NTC
thermistor. The chip type NTC thermistor can be easily disposed to be
close to the chip type light emitting element 91 illustrated in FIG. 12,
and the distance therebetween is easily shortened. For this reason, an
area which contributes to the heat conduction between the light emitting
element 91 and the temperature variable resistive element 92 becomes
large. As a result, the thermal conductivity between the light emitting
element 91 and the temperature variable resistive element 92 increases.
Therefore, it is possible to reduce a time difference between the light
emitting element 91 and the temperature variable resistive element 92 as
the temperature increases. Accordingly, after the amount of light of the
light emitting element 91 exceeds the certain value, a time lag until the
resistance value of the temperature variable resistive element 92 is
sufficiently small and the current decreases to an extent that the amount
of light of the light emitting element 91 is lower than the certain
value, is reduced. This also causes the time for emitting the light
having an amount that adversely affects the retina to be a minimum.
Accordingly, it is possible to further enhance safety of the light
emitting device 9.

[0180] In addition, in the light emitting device 9 illustrated in FIG. 12,
the light emitting element 91 and the temperature variable resistive
element 92 are insulated via a layer-shaped insulator 95. For this
reason, even when the light emitting element 91 and the temperature
variable resistive element 92 are disposed close to each other, while
preventing the generation of a failure, such as a short circuit, it is
possible to enhance the thermal conductivity between the light emitting
element 91 and the temperature variable resistive element 92.

[0181] In addition, from such a viewpoint, as an insulator 95, it is
preferable to use a member which has a thermal conductivity. Examples of
the insulator 95 having a thermal conductivity include ceramics, a
thermally conductive grease, a thermally conductive adhesive, a thermally
conductive tape, or the like. Among these, in the viewpoint of insulation
properties and adhesiveness, it is preferable to configure the insulator
by an epoxy resin or a polyimide resin. Even in a case of the resin
material, by making the thickness of the insulator 95 thin, it is
possible to sufficiently ensure the thermal conductivity. In addition, in
order to enhance the thermal conductivity, there is even a case where a
certain amount of conductive particles is added as necessary.

[0182] The temperature variable resistive element 92 illustrated in FIG.
12 is an example of the chip type NTC thermistor, and is provided with a
thermistor prime field 921 and a pair of terminal electrodes 922 and 923
which is provided on an upper surface thereof. The thermistor prime field
921 is configured by the semiconductor material which has an oxide of a
transition metal, such as manganese, nickel, or cobalt, as a main
component. As the temperature of the thermistor prime field 921 changes,
the resistance value between the terminal electrode 922 and the terminal
electrode 923 changes. In addition, as an internal electrode is provided
in the thermistor prime field 921 as necessary, the thermistor prime
field 921 may have a lamination structure.

[0183] In addition, the terminal electrode 922 and the lower electrode 912
of the light emitting element 91 are electrically connected to each other
via a bonding wire 987. Meanwhile, the terminal electrode 923 and the
upper electrode 913 of the light emitting element 91 are electrically
connected to each other via a bonding wire 988.

[0184] In addition, in the light emitting device 9 illustrated in FIG. 12,
both the light emitting element 91 and the temperature variable resistive
element 92 are mounted on the mount 93. For this reason, while the heat
from the light emitting element 91 can be conducted to the temperature
variable resistive element 92, the heat can be conducted to the mount 93.
Since the mount 93 generally has a relatively high heat capacity, it is
possible to contribute to dissipating the heat of the light emitting
element 91.

[0185] Meanwhile, the layer-shaped insulator 95 is interposed between the
temperature variable resistive element 92 and the mount 93. Accordingly,
even when the mount 93 has a conductivity, it is possible to prevent a
short circuit between the temperature variable resistive element 92 and
the mount 93. In addition, as the insulator 95 has a heat conductivity,
heat dissipation properties of the temperature variable resistive element
92 are improved. As a result, it is possible to avoid a failure in which
the heat conducted from the light emitting element 91 to the temperature
variable resistive element 92 remains in the temperature variable
resistive element 92, and the temperature change of the temperature
variable resistive element 92 does not sufficiently conform with the
temperature change of the light emitting element 91.

[0186] In addition, in the light emitting device 9 according to the
embodiment, both the above-described light variable resistive element 97
and the temperature variable resistive element 92 are used. It is
possible to secure safety based on two different principles which are a
principle in which the light is used and a principle in which the heat is
used, and to particularly enhance security of the light emitting device
9. In addition, for example, it is possible to detect a failure of the
light emitting element 91 in which the amount of light does not increase,
but a heating amount increases. In other words, as the light variable
resistive element 97 and the temperature variable resistive element 92
are respectively connected to the resistive element 96 (refer to FIG. 11)
in series, it is possible to easily detect the current which flows
through each line. For this reason, when an increase amount of light and
an increase amount of heating are compared, and the increase amount of
heating is extremely large, it is possible to confirm that there is a
failure in the light emitting element 91.

[0187] In addition, in the light emitting device 9 illustrated in FIG. 12,
as the temperature increases, a time difference which is difficult to be
compensated is generated between the light emitting element 91 and the
temperature variable resistive element 92. During this short period of
time, the amount of light of the light emitting element 91 remains to be
above the certain value. Meanwhile, if the time period is short like
this, even when the amount of light is above regulatory limits, it is
considered that an adverse effect on the retina is small.

[0188] Here, during the short time period until the current which flows in
the light emitting element 91 is defined, the light having a large amount
is emitted from the light emitting element 91. Therefore, in the light
emitting device 9, the light having a large amount may be used as light
which is emitted to send a command of warning. As such a warning (alarm)
is generated, the user of the light emitting device 9, that is, the user
of the image display apparatus 1 can know of an abnormality of the light
emitting device 9. For example, it is possible to obtain a chance to take
an action, such as restraining the use of the apparatus for a certain
period of time, or inspecting and repairing the light emitting device 9.

[0189] Even in the fifth embodiment, similar operations and effects to
those of the first embodiment can be obtained.

[0190] Above, the light emitting device and the image display apparatus
according to the invention is described based on the embodiments
illustrated in the drawing. However, the invention is not limited
thereto.

[0191] For example, in the light emitting device and the image display
apparatus according to the invention, the configurations of each part can
be replaced with an arbitrary configuration which shows similar
functions. In addition, an arbitrary configuration can be added.

[0192] In addition, among the above-described embodiments, two or more
embodiments may be combined. For example, the resistive element according
to the fourth embodiment may be added to the light emitting device
according to the first embodiment.

[0193] In addition, not limiting to the end surface light emitting type
semiconductor laser, a surface light emitting type semiconductor laser
can be used as the semiconductor laser. The surface light emitting type
semiconductor laser has a configuration in which the resonator for
resonating the light is perpendicular to the semiconductor substrate
surface. The surface light emitting type semiconductor laser has high
light emitting efficiency compared to the end surface light emitting type
semiconductor laser. In addition, since fast modulation is possible, the
surface light emitting type semiconductor laser is advantageous as a
light emitting element which is used, in particular, in the image display
apparatus.